1.知识点：能够对比以下的录屏进行阅读
SQL> -- 查询10和20号部门的员工的3种方法
SQL> --1. select * from emp where deptno in (10,20);
SQL> --2. select * from emp where deptno=10 or deptno=20;
SQL> --3. 集合运算：union/union all并集。intersect 交集；minus差集
SQL> -- select * from emp where deptno=10
SQL> -- +
SQL> -- select * from emp where deptno=20;
SQL> --union：并集，反复的区域仅仅取一次；union all：并集。反复的区域取两次
SQL> select * from emp where deptno=10
2 union
3 select * from emp where deptno=20;SQL> --利用集合运算实现group by的增强
SQL> --注意
SQL> --1. 參与运算的各个集合必须列数同样 且类型一致
SQL> --2. 採用第一个集合的表头作为最后的表头
SQL> --3. 假设排序。必须在每一个集合后使用同样的order by
SQL> --4. 能够使用括号
SQL> select deptno,job,sum(sal) from emp group by deptno,job
2 union
3 select deptno,to_char(null),sum(sal) from emp group by deptno
4 union
5 select to_number(null),to_char(null),sum(sal) from emp;SQL> --打开sql运行时间，每次运行sql语句都会显示运行时间
SQL> set timing on
SQL> --关闭sql运行时间
SQL> set timing offSQL> --交集：既属于intersect前面的集合又属于intersect后面的集合
SQL> select ename,sal from emp
2 where sal between 700 and 1300
3 INTERSECT
4 select ename,sal from emp
5 where sal between 1201 and 1400;SQL> --差集：仅仅属于minus前面的集合而不属于minus后面的集合
SQL> select ename,sal from emp
2 where sal between 700 and 1300
3 minus
4 select ename,sal from emp
5 where sal between 1201 and 1400;
2.在Sqlplus下实际运行的结果录屏
SQL> /*
SQL> 查询10和20号部门的员工
SQL> 1. select * from emp where deptno in (10,20);
SQL> 2. select * from emp where deptno=10 or deptno=20;
SQL> 3. 集合运算
SQL> select * from emp where deptno=10
SQL> +
SQL> select * from emp where deptno=20;
SQL> */
SQL> select * from emp where deptno=10
2 union
3 select * from emp where deptno=20; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- -------------- ----- ---------- ------
7369 SMITH CLERK 7902 17-12月-80 800 20
7566 JONES MANAGER 7839 02-4月 -81 2975 20
7782 CLARK MANAGER 7839 09-6月 -81 2450 10
7788 SCOTT ANALYST 7566 13-7月 -87 3000 20
7839 KING PRESIDENT 17-11月-81 5000 10
7876 ADAMS CLERK 7788 13-7月 -87 1100 20
7902 FORD ANALYST 7566 03-12月-81 3000 20
7934 MILLER CLERK 7782 23-1月 -82 1300 10 已选择8行。SQL> --利用集合运算实现group by的增强
SQL> select deptno,job,sum(sal) from emp group by deptno,job
2 union
3 select deptno,sum(sal) from emp group by deptno
4 union
5 select sum(sal) from emp;
select deptno,sum(sal) from emp group by deptno
*
第 3 行出现错误:
ORA-01789: 查询块具有不对的结果列数 SQL> /*
SQL> 注意
SQL> 1. 參与运算的各个集合必须列数同样 且类型一致
SQL> 2. 採用第一个集合的表头作为最后的表头
SQL> 3. 假设排序，必须在每一个集合后使用同样的order by
SQL> 4. 能够使用括号
SQL> */
SQL> select deptno,job,sum(sal) from emp group by deptno,job
2 union
3 select deptno,to_char(null),sum(sal) from emp group by deptno
4 union
5 select to_number(null),to_char(null),sum(sal) from emp;DEPTNO JOB SUM(SAL)
------ --------- ----------
10 CLERK 1300
10 MANAGER 2450
10 PRESIDENT 5000
10 8750
20 ANALYST 6000
20 CLERK 1900
20 MANAGER 2975
20 10875
30 CLERK 950
30 MANAGER 2850
30 SALESMAN 5600 DEPTNO JOB SUM(SAL)
------ --------- ----------
30 9400
29025 已选择13行。SQL> break on deptno skip 2
SQL> select deptno,job,sum(sal) from emp group by deptno,job
2 union
3 select deptno,to_char(null),sum(sal) from emp group by deptno
4 union
5 select to_number(null),to_char(null),sum(sal) from emp;DEPTNO JOB SUM(SAL)
------ --------- ----------
10 CLERK 1300
MANAGER 2450
PRESIDENT 5000
8750 20 ANALYST 6000
CLERK 1900
MANAGER 2975
10875 DEPTNO JOB SUM(SAL)
------ --------- ---------- 30 CLERK 950
MANAGER 2850
SALESMAN 5600
9400 29025 已选择13行。SQL> break on null
SQL> select deptno,job,sum(sal) from emp group by rollup(deptno,job);DEPTNO JOB SUM(SAL)
------ --------- ----------
10 CLERK 1300
10 MANAGER 2450
10 PRESIDENT 5000
10 8750
20 CLERK 1900
20 ANALYST 6000
20 MANAGER 2975
20 10875
30 CLERK 950
30 MANAGER 2850
30 SALESMAN 5600 DEPTNO JOB SUM(SAL)
------ --------- ----------
30 9400
29025 已选择13行。SQL> --打开sql运行时间
SQL> set timing on
SQL> select deptno,job,sum(sal) from emp group by rollup(deptno,job);DEPTNO JOB SUM(SAL)
------ --------- ----------
10 CLERK 1300
10 MANAGER 2450
10 PRESIDENT 5000
10 8750
20 CLERK 1900
20 ANALYST 6000
20 MANAGER 2975
20 10875
30 CLERK 950
30 MANAGER 2850
30 SALESMAN 5600 DEPTNO JOB SUM(SAL)
------ --------- ----------
30 9400
29025 已选择13行。已用时间: 00: 00: 00.00
SQL> select deptno,job,sum(sal) from emp group by deptno,job
2 union
3 select deptno,to_char(null),sum(sal) from emp group by deptno
4 union
5 select to_number(null),to_char(null),sum(sal) from emp;DEPTNO JOB SUM(SAL)
------ --------- ----------
10 CLERK 1300
10 MANAGER 2450
10 PRESIDENT 5000
10 8750
20 ANALYST 6000
20 CLERK 1900
20 MANAGER 2975
20 10875
30 CLERK 950
30 MANAGER 2850
30 SALESMAN 5600 DEPTNO JOB SUM(SAL)
------ --------- ----------
30 9400
29025 已选择13行。已用时间: 00: 00: 00.01
SQL> set timing off
SQL> select ename,sal from emp
2 where sal between 700 and 1300
3 INTERSECT
4 select ename,sal from emp
5 where sal between 1201 and 1400;ENAME SAL
---------- -----
MARTIN 1250
MILLER 1300
WARD 1250 SQL> select ename,sal from emp
2 where sal between 700 and 1300
3 minus
4 select ename,sal from emp
5 where sal between 1201 and 1400;ENAME SAL
---------- -----
ADAMS 1100
JAMES 950
SMITH 800 SQL> spool off
